1. Characterization of the expression profile of catalases ofVibrio parahaemolyticus in response to oxidative stress Catalases act to protect microorganisms from oxidative stress by degrading hydrogen peroxide. This study identified four types of catalase in Vibrio parahaemolyticus on the basis of zymographic analysis, which we have named A to D according to their migration pattern in a native gel. Our results show that while catalase B is stable at 55°C after 15 min of incubation, the other three catalases are unstable at this temperature. The expression levels of catalases A and B were found to be induced in response to hydrogen peroxide during the log phase; however, their expression declined after the cells entered the stationary phase. Catalases C and D were also found to have peroxidase activity, indicating that these two enzymes are bifunctional catalases. While catalases C and D were found to be expressed only during the stationary phase and not during the log phase, culturing the cells under pH 5.5 and starvation conditions induced their expression. This study has also shown that the expression of catalases C and D depends on RpoS, a general stress response regulator. The findings of this study show that V. parahaemolyticus expresses multiple catalases that allow it to survive in a variety of environments.

2. Characterization and genomic analysis of a N4-like vibriophage

Marine phages are the most abundant entities in the world. It was estimated approximately 10 million particles per milliliter. They are contributed to the dynamic changes of microbial community structure and diversity, and also play significant role in horizontal gene transfer. More importantly, the mortality of marine microorganisms mediated by phages directly affects nutrient and energy cycles in the open sea. Vibrios are common inhabitants of aquatic environments and have been reported on its association with the health of corals. In order to study the microorganism community changes upon phage predation, we isolated vibriophage and its host from macroalgae in intertidal zones in Hualien. We currently focus on Vibrio communis and its related phage, phi50-12. Vibrio communis is a widespread species and frequently isolated from marine environment. phi50-12, belongs to Podoviridae, having a 70 nm icosahedral capsid with short tail. According to the genomic sequence of phi50-12 revealed it is a N4 like phage. A detail study of the interaction between phi50-12 and host V. communis will be determined further.